[Elecraft] Crystal ovens

[Rich Haendel]

Yes, crystal ovens are used to stabilize the temperature of a crystal so it doesn't drift.  BUT, there is a caveat.  Crystals used for oven operation are cut differently than those used without ovens.  That is,  the inflection point of the crystal frequency offset verses  temperature is manufactured so that the oven temperature is at this same inflection point.  Imagine an upside down "U".  Example: The oven is set to operate at a temperature above what the equipment internal temperature is expected to be.  Lets say that the oven temperature is specified at 60 degrees C.  Then the crystal temperature inflection point (peak of the "U" ) is matched to 60 degrees.  This way temperature cycling of the oven over a few degrees will not change the operating frequency of the crystal, if at all.  Crystals designed for ambient operation have a different temperature curve, more like a "S" laid down on its back.  Why crystals are cut this way is so that there is a minimum frequency shift over a wide temperature range. Typical AT-cut crystals have a first minimum frequency  point near -10 to -25 degrees C and a second maximum frequency point about 40-50 degrees C.  

Rich Haendel W3ACO